Drawing and bulking of synthetic filament yarns

ABSTRACT

In a process for producing false twist crimped synthetic yarn from crimpless undrawn yarn comprising: partially drawing the crimpless undrawn yarn to less than full extent; imparting potential crimp by immediately and continuously imparting false twist to the partially-drawn yarn and heating the same under sufficient tension to complete the drawing; and releasing the tension.

United States Patent inventors App]. No.

Filed Patented Assignee Priority DRAWING AND BULKING OF SYNTHETICFILAMENT YARNS 7 Claims, 1 Drawing Fig.

US. Cl 57/157 Int. Cl D023 1/00, D02g i/02 Field 0| Search 57/34, 36,

Fabnb new! (more: per syua/eynm A x 3;

[56] References Cited UNITED STATES PATENTS 3,365,874 1/1968 Chidgey eta1. 57/157 3,404,525 10/1968 Tomkins 57/157 X 2,671,304 3/1954 Rowedder57/51 2,890,568 6/1959 Willens 57/34 X 3,400,194 9/1968 Boone et al.57/157 X 3,435,603 4/1969 Rice 57/34 3,457,338 7/1969 Lefevre 57/55.5 X3,474,612 10/1969 Jenkins et al. 57/34 FOREIGN PATENTS 777,625 6/1957Great Britain 57/34 815,202 6/1959 Great Britain 57/157 PrimaryExaminer-Donald E. Watkins Attorney-Cushman, Darby & Cushman .525 0fiat/0 of draw l n /0 mfa/se DRAWING AND BULKING or SYNTHETIC FILAMENT 1YARNS The invention concerns improvements in or relating to the drawingand bulking of synthetic filament yarns.

A widely employed method of bulking synthetic filament yarns is themethod known as false twist crimping, in which a temporary, or falsetwist is continuously imparted to a running yarn the twist is set byheating means, and then the yarn is detwisted in a sense to remove thetemporary twist. However, because the twist has been set, the finaldetwistingof the twistset yarn causes the filaments to crimp and cookie,and it is this operation which imparts bulk to the yarn, although thebulk may only be latent until some process to make it manifest has beenperformed on the yarn such as a heat treatment under conditions ofcontrolled relaxation.

False twist crimping may be carried out on synthetic filament yarnsupplied on packages in the fully drawn condition, i.e. the yarn hasbeen packaged by the producer after the standard drawing process hasbeen carried out, in which the undrawn yarn as spun from the spinningmachines is extended by several times its undrawn length to orient themolecules.

Alternatively, it is known to combine the drawing and the false twistcrimping stages on one machine, so that a package of undrawn yarn isfirst submitted to a standard drawing treatment and then the drawn yarnis immediately fed into the false twist crimping stage.

Yet another alternative is to submit undrawn yarn from a supply thereofto such conditions of tension in a false twist crimping process that theyarn is both drawn and crimped thereby.

This latter method has been found to be the better one of the twomethods starting with an undrawn yarn supply from the point of view ofthe bulking effect at a given throughput. Nevertheless, there is sometendency for filaments to be broken; and also the bulked yarn seems toimpart a glittery effect to fabric which may not be desirable. Thesepotential defects are not present in yarn bulked by the former of thetwo methods starting with an undrawn yarn supply, i.e. the method inwhich the yarn is normally drawn before being fed into the false twistcrimping stage; but, in order to attain a given level of bulk in yarnprocessed by this method, it is necessary to run the process at a lowerthroughput. Hence, the machines are not employed to their full capacity.

We have now discovered that the above mentioned potential defects foundwhen undrawn yarn is directly false twist crimped and drawn can beameliorated if the yarn is first predrawn to a less than full extent,and then the final amount of drawing, only, is performed coincidentallywith the false twist crimping.

Accordingly, the invention comprises a process for false twist crimpinga synthetic filament yarn, in which process the synthetic filament yarnin undrawn condition is firstly submitted to a predrawing stage in whichthe yarn is drawn by less than the full amount, and then thepartially-drawn yarn is fed to a false twist crimping stage under suchconditions of tension that drawing of the yarn is completed whilst theyarn is heated in said false twist crimping stage.

it is presently preferred to operate under conditions such that thetotal draw ratio achievable is not reduced much below that normallyachieved when either of the two known methods are employed, i.e. whenthe yarn is either fully predrawn or is wholly drawn on the false twistcrimping heater. This entails operating at either end of the scale, i.e.at the end where the yarn is nearly fully drawn during predrawing, or atthe other end when only very slight predrawing is performed.

The invention may be illustrated with reference to the attached drawingwhich shows diagrammatically the relationship for poly(hexamethyleneadipamide) between fabric weight and the ratio of the draw ratio in thefalse twist crimping stage to the draw ratio in the predrawing stage.This relationship was obtained by processing a filament supply yarn ofpoly(hexamethylene adipamide) at a throughput speed of 1700 feet/minute,the undrawn denier being 211 to be drawn to a nominal 70 denier. Theweight of fabric per square yard, which is a measure of bulk, wasdetermined for twofold 70 denier yarns knitted in an 18 gauge interlockfabric with a stitch length of 0. 144 inches.

As illustrated in the FIGURE high bulk may be obtained when the ratio ofthe two draw ratios is. selected in the range 0.3 to 0.8 or when theratio is above. 1.3. The upper limit for the ratio is determined by thedesirability of avoiding the glittery effect imparted to fabric whenundrawn yarn is both drawn and crimped in a false twist crimpingprocess. Hence, it is essential that some drawing takes place in apredrawing stage. We have found that values for the ratio of the twodraw ratios up to about 2.8 are particularly useful.

The invention is applicable to all synthetic filament yarns capable ofbeing heat-set and is particularly applicable to polyamide yarns such aspoly(hexamethylene adipamide) yarns.

The polyamide yarn may be derived from a polyamide polymer of a kindwhich has been nucleated with calcium fluoride in such manner that themean maximum nucleant separation distance is given by the expressionwhere- G is the linear rate of crystallization at a temperature T S isthe mean maximum nucleant separation distance and KC is the distance ofthe solidification point from the spinneret for unnucleated polymer when:spun into filaments.

The use of a yarn derived from such a nucleated polymer enables higherthroughput speeds to be used in the present invention as compared withthe use of a yam derived from an unnucleated polymer.

The invention is not limited by the means adopted for drawing and forfalse twist crimping. Nevertheless, it is preferred to predraw the yarnbetween a feed roll and a faster rotating draw roll whilst localizingthe point of draw at a ceramic snubbing-pin; and it is preferred to fedthe predrawn yarn directly into the false twist crimping zone by andfrom said draw roll, with the false twist being imparted directly to theyarn by a rotary friction device. The yarn is then withdrawn from thefriction device at a speed greater than that at which it was fed theretoby the draw roll. The false twist is set, and the final drawing iscarried out, while the yarn is passing through or over the heater of thefalse twist crimping zone.

It is, of course, possible to carry out bulk-development or otherpost-treatments on the false twist crimped yarn either concurrently orat some later stage in yarn or fabric production. Thus, bulk may bedeveloped by heat treating the false twist crimped yarn under acontrolled tension and temperature.

What we claim is:

1. In a process for producing a false twist crimped synthetic filamentyarn the improvement consisting in firstly submitting the syntheticfilament yarn in undrawn condition to a predrawing stage in which theyarn is drawn by less than the full amount and then feeding thepartially-drawn yarn to a false twist crimping stage under suchconditions of tension that drawing of the yarn is completed, whilst theyarn is heated in said false twist crimping stage.

2. A process according to claim 1 in which the synthetic filament yarnis a polyamide yarn.

3. A process according to claim 2 in which the synthetic filament yarnis poly(hexamthylene adipamide) yarn.

4. A process for developing bulk in a false twist crimped syntheticfilament yarn made by a process according to claim l in which processthe false twist crimped yarn is heat treated under a controlled tensionand temperature.

5. A process according to claim 3 in which the ratio of the draw ratioin the false twist crimping stage to the draw ratio in the predrawingstage lies in the range 0.3 to 0.8.

6. A procels as in claim 3 in which the draw ratio in the false twistingcrimping stage at the draw ratio in the predrawing stage is above 1.3. I

7 In a process for producing false twist crimped synthetic yarn fromcrimpless undrawn yarn comprising: partially drawing the crimplessundrawn yarn to less than full extent; impart-

2. A process according to claim 1 in which the synthetic filament yarnis a polyamide yarn.
 3. A process according to claim 2 in which thesynthetic filament yarn is poly(hexamthylene adipamide) yarn.
 4. Aprocess for developing bulk in a false twist crimped synthetic filamentyarn made by a process according to claim 1 in which process the falsetwist crimped yarn is heat treated under a controlled tension andtemperature.
 5. A process according to claim 3 in which the ratio of thedraw ratio in the false twist crimping stage to the draw ratio in thepredrawing stage lies in the range 0.3 to 0.8.
 6. A process as in claim3 in which the draw ratio in the false twisting crimping stage at thedraw ratio in the predrawing stage is above 1.3.
 7. In a process forproducing false twist crimped synthetic yarn from crimpless undrawn yarncomprising: partially drawing the crimpless undrawn yarn to less thanfull extent; imparting potential crimp by immediately and continuouslyimparting false twist to the partially-drawn yarn and heating the sameunder sufficient tension to complete the drawing; and releasing thetension.